ABSTRACT
A cobalt-diphosphine catalyst has been found to promote a selective 1:2 coupling reaction between aldehydes and allenes to form ß,δ-dialkylidene ketones, featuring skipped diene moieties, with high regioselectivities and stereoselectivities. The reaction is distinct from previously reported, rhodium-catalyzed aldehyde-allene 1:2 coupling to afford ß,γ-dialkylidene ketones bearing 1,3-diene moieties. The present hydroacylative dimerization involves a unique allene/allene oxidative cyclization mode to form a C1-C2 linkage between the allene molecules.
ABSTRACT
Mechanochemistry is a green, solid-state, re-emerging synthetic technique that can rapidly form complex molecules and materials without exogenous heat or solvent(s). Herein, we report the application of solvent-free mechanochemical ball milling for the synthesis of metal halide perovskites, to overcome problems with solution-based syntheses. We prepared phase-pure, air-sensitive CsSnX3 (X = I, Br, Cl) and its mixed halide perovskites by mechanochemistry for the first time by reactions between cesium and tin(II) halides. Notably, we report the sole examples where metastable, high-temperature phases like cubic CsSnCl3, cubic CsPbI3, and trigonal FAPbI3 were accessible at ambient temperatures and pressures without post-synthetic processing. The perovskites can be prepared up to "kilogram scales." Lead-free, all-inorganic photodetector devices were fabricated using the mechanosynthesized CsSnBr1.5Cl1.5 under solvent-free conditions and showed 10-fold differences between on-off currents. We highlight an essentially solvent-free, general approach to synthesize metastable compounds and fabricate photodetectors from commercially available precursors.
